In recent years the development of high electron mobility transistors (HEMTs) in which a gallium nitride (GaN) layer functions as an electron transit layer has advanced.
GaN has a band gap of about 3.4 eV which is wider than the bad gap (1.1 eV) of silicon (Si) or the band gap (1.4 eV) of gallium arsenide (GaAs). Accordingly, the breakdown voltage of GaN-based HEMTs (GaN-HEMTs) is higher than that of Si-based or GaAs-based devices and GaN-HEMTs are considered to be promising as high breakdown voltage power devices.
On the other hand, if a surge occurs, then a failure or the like may occur in a GaN-HEMI. Accordingly, a measure to effectively suppress a surge is required.
In the past a technique for suppressing surge voltage by exercising control so as to return to a power supply a charging electric charge in a snubber circuit connected to a switching element which performs high-frequency switching of an inverter apparatus was proposed. Furthermore, a technique for changing a drain-source state from a conducting state to a cutoff state by applying photoelectromotive force generated by a light receiving element to a transistor was proposed.
International Publication Pamphlet No. WO2011/067838
Japanese Laid-open Patent Publication No. 2002-353798
In the past a circuit in which an inductor and a capacitor are combined was used as an anti-surge measure. For example, the following technique is possible. A reactor (inductor) in a regeneration circuit corresponding to a switching element resonates with a snubber capacitor in a snubber circuit. As a result, a charging electric charge of the snubber capacitor is returned to a power supply to suppress surge voltage.
However, the size of an inductor is large among passive elements and its mounting area is also large. Accordingly, the scale of a circuit in which an inductor is used is large.